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Influenza Virus
Influenza viruses are the cause of acute
respiratory disease known as influenza or 'flu' in man and
animals. The viruses are classified as members of the family
Orthomyxoviridae because of their ability to bind to mucus. Based
on the antigenic nature of their surface glycoproteins
haemagglutinin (HA) and neuraminidase (NA) the Orthomyxoviridae
are divided into two genera: influenza A and B viruses, and
influenza C virus. The three virus types can be distinguished
from one another on the basis of antigenic differences between
their nucleoproteins and matrix proteins. Influenza A viruses
infect a wide range of avian and mammalian species. The type A
viruses are further divided into subtypes. (H1→H16, N1→N9) They
have a spherical or filamentous morphology and are medium-sized,
with a diameter of 80 to 120 nm. The lipid membrane of the
virion, envelop, is derived from the host cell in which the virus
replicated. There are two transmembrane glycoproteins HA and NA,
called spikes. M2 or matrix protein 2 is a third transmembrane
protein are present about 20 to 60 copy per virion. Another
protein, named M1, forms a layer Beneath the envelop and
encapsidates the ribonucleoprotein complexes. Two non-structural
proteins, NS1 and NS2, are also associated with the virus. The
influenza virus genome consists of eight unique segments of
single-stranded RNA which have negative polarity. |
